Digestion of raw materials



April 14, 1931.

S. MILNE DIGESTION 0F RAW MATERIALS Filed March 16, 1928 Patented Apr. 14, 1931 UNITED STATES SAMUEL MILNE, OF EDINBURGH, SCOTLAND DIGESTICN OF MATERIALS Application flledKarch 16, 192$,S61il1 No.262,265, and in Great Britain March 26, 1927.

This invention relates to;processes involving chemical re-actions with the cell contents of natural organized materials and has for its object the control of the desired chemical 5 reaction with a suitable, applied reagent.

The invention consists in the manufacture of products by chemical re-action between a suitable, applied re -agent and the cell con tents of anatural organized material, (fibrous or otherwise) wherein the re-action is controlled by the application thereto of an externally generated, relatively high frequency, transient, electro-motive force.

One application of the invention is in the acceleration of the re-actionsinithe digestion of raw fibrous materials for paper making and like purposes.

The acceleration ofvthe reactions is observed in one or some of thefollowing effects,

2 considerable shortening of the time, reduction in the quantity of :the applied re-agent required for digestioma very much more complete removal of the non-cellulose matter required to be eliminated,rthe rendering effective of a re-agent ordinarily ineffective or relatively ineflectivewand the suppression of unwanted re-actions.

Various experiments have been made to obtain effective application of the necessary, transient, electrosmotive force for the acceleration of the re-actions in digestion, and the means employed for such applicationhave produced various degrees of effect.

The accompanying drawings illustrate diagrammatically various electrical arrangements for the different experiments which will hereinafter be described,in which Figs. 1, 2 and 2a illustrate the first series of experiments.

Figs. 3, 4 and 5 illustrates, further series of experiments employing induction.

In one experiment on alaboratory scale a small steel digester cylinder was used, holding about eight ounces of dry material, which could be closed and in which the pressure and temperature conditions could bemaintained approximating to the conditions in i a full sized commercial digester. Thedigester was charged with five ounces of grass andthirty ounces of liquorcontaining haltiamounce :of

caustic soda (commercial)- The digester a see Fig. l was stood on a gas ring I) and was grounded through a coil of wire 0 of about 25 turns. The time for the experiment was chosen when the local broadcasting wireless station was transmitting. The gas was lighted and the digester heated to 280 F. and maintained atthis temperature for '30 min utes. When cool the digester was opened and the pulp appeared to be exceptionally well so; cooked. (in washing it wasifound that the non cellulose matter was completely removed, and the pulp was a noticeablylightcolour. When tested for bleaching it was found to bleacheasily to a full white. This experiment was repeated frequently with unvaryingly successfulresults.

Subsequently still further improvements Were effected in the results by theuse of other means for applying the transient, electromotive force, which means employedthe same source of power, namelyelectrical oscillations obtainable from wirelesstransmission, such means consisting in the use of an aerial d (see Fig. 2) and a series condenser e, by which the aerial circuit could be tuned, connected to the top'ofthe digester a, the bottom of the diges ter being earthed, either directly or through a coil 7 (see Fig. 2a), the best results however being obtained with a coil in the earth circuit. v

The essential points which stand out in these experiments are the small values of the applied, transient,electro-motive force and the high frequency thereof. 7

The application of the methods employed in commercial processes presents several difficulties, in particular in obtaining the insulation of the digester for the inter-position of a coil in the earth circuit. "This difficulty is not however insuperable as with high frequency currents the digester,thoughearthed, is relatively insulated bythe impedance of the earth circuit and by its own capacity. Considering the digester and its connections as an oscillating circuit, its resistance and therefore its insulation, will be maximum when the applied, oscillating, electro-motive force is in resonance therewith and therefore when ice terminals on and n of a two volt accumulator force was applied to its contents by placing an insulated wire or an insulated metal plate 9 (see Fig. 3) around the digester, forming as it were a condenser element. This element was connected by a commutator h and brushes 9' and k to the positive and negative in the case of which was inserted a cadmium plate 0 which was connected to earth. The commutator was rotated by an electric motor (not shown) to give contact with each terminal about 80 times a minute. The positive and negative terminals of the accumulator relative to the cadmium plate and therefore to earth, have a positive potential of 2.24 volts and 0.14 volts respectively, and therefore the positive charge on the plate 9 is changed 160 times a minute. With each change of charge on the condenser are produced damped oscillations which provide the necessary transient electro-motive force. This experiment was ultimately tested on a 5 ton digester with results which indicated considerable acceleration of the re-actions. Experiments are in progress to ascertain the relations (if any) between the size of the condenser, the voltage changes, the frequency of the voltage changes, the proportional quantity of the re-agent and time of the cook,

and further to ascertain as far as possible the optimum conditions.

The experiments so far made indicate the desirability of a large area of condenser and small voltage changes and the possibility of a reduction of 33 per cent. of the re-agent and 50% reduction of time.

In other experiments on the same lines an. accumulator was used to provide the voltage for charging the condenser plate and the terminals of the accumulator were connected to give voltage changes from 4 volts to 2 volts (see Fig. 4:) and from 6 volts to 4 volts (see Fig. 5), and for other values and with equally promising results. By this means the necessity for the use of the cadmium cell was avoided, and beneficially as this threat- "ened to present trouble in maintenance.

A characteristic feature of each cook was that whereas ordinarily the pulp stood as a solid cone in the centre of the digester, it now always assumed a concave form spreading up the sides of the digester. Further, the operatives remarked on the ease of discharging and refilling of the digester as compared with the other and like digesters, also upon the ease of washing the pulp and the extreme regularity of the cook. The finequality and colour of the pulp was also noticeable, as well as the ease with which it would bleach, the grass used being Esparto.

An important feature was that the charge on the condenser must never be negative or other and, (for the purpose of digestion), undesirable re-actions were stimulated, and that the maintenance of a positive charge was beneficial. Obviously there are other ways by'which an electrician could arrange for the required charges and changes thereof. It was noticed that the use of a potentiometer however,.to supply the respective voltages, was relatively a failure owing probably to the heavy-damping of the charge and discharge the important factor being the shock ofv charge and discharge producing high frequency oscillations, the frequency of-wbich depended upon the natural frequency of the various circuits. I p x 7 Results have been successfully obtained with the condenser placed within the digester, but insulation difficulties in maintenance will naturally be against such an application.

It is not possible .at this stage to assign specific frequencies of oscillations for particular effects nor to state any-limits for the intensity of potential which may be used.

It must be clearly understood that the control obtained by this invention is entirely distinct from any electrolytic action-and further that electrolytic actionis to be avoided metal parts of thevessel', pipes, etc. from the normal action of the acid. ;This is a commercial advantage for which no specific claim is made. 7 p

'What I claim is:'---- '1. The process, in the manufacture of products by chemical reaction between a suitable applied reagent'and the cell contents of a natural organized material,for controlling the reaction, consisting in the application'of an externally generated relatively high-frequency, transient, electromotive force.

2. The manufactureof products according to claim 1, characterizedin that the mass of the reaction is electrically earthed 'and' in that the controllingenergy is applied by induction.

- [3. The manufacture of products according to claim 1. characterized in that the mass of the reaction is electrically earthed and in that the controlling energy is applied inductively by means of an adjacent insulated condenser element to which the electro-motive force is applied from an oscillating electric circuit.

4. The process according to claim 1, further characterized by the application of an electrical bias-potential, as set forth.

5. The process of digestion of raw materials for the manufacture of paper, wherein the reaction is conducted in an iron digester, electrically connected to earth and wherein the digestive reactions are accelerated by the inductive effect of a relatively high-frequency transient electrical potential applied to an adjacent element, as set forth.

6. The process of digestion of raw materials according to claim 5, characterized by the application of a positive bias-potential to the said adjacent element, as set forth.

7. The process of digestion of raw materials according to claim 5, further characterized in that the said element comprises an electrically conductive insulated plate, as set forth.

8. In the manufacture of products by chemical reaction between a suitably applied reagent and the cell contents of a natural organized material, the application thereto of an externally generate-d relatively highfrequency transient electro-motive force by means of a tuned oscillating electric circuit, as set forth.

In testimony whereof I have signed my name to this specification.

SAMUEL MILNE. 

